In well drilling, with a rotary drilling rig, the drill bit and drilling pipe receive rotary motion from power equipment located on the surface. Below the drilling floor, at the ground surface, there is usually an assembly known as a drilling head that provides means for the circulation of various fluids used in the drilling.
U.S. Pat. No. 3,400,938, issued Sept. 10, 1960, discloses a drilling head assembly including means for assisting a circulation of lubricant around thrust bearings and sealing such bearings from well fluids and other debris. The circulation of lubricant around the bearings is assisted by providing annular recesses adjacent the bearings but is such as does not provide forced lubrication of the bearings.
The provision of forced circulation of lubricant for bearings journaling a shaft for rotation about a vertical axis is examplified by U.S. Pat. Nos. 1,157,644, issued Oct. 19, 1915 and 4,037,890, issued July 26, 1977. The former patent is provided with a bushing secured to the shaft for rotation therewith, which bushing has on its exterior surface spiral grooves which feed lubricant upwardly toward the bearing within which the shaft is journaled. The latter patent is directed to utilizing a spiral groove pump, also situated beneath the bearing, to pump lubricating oil downwardly into a lubricant reservoir extending upwardly to a point above the bearing whereby lubricating oil is caused to overflow downwardly into the bearing.
In U.S. Pat. No. 3,061,387, issued Oct. 30, 1962, there is disclosed in conjunction with a bearing for a vertically rotatable shaft the provision of a vertically disposed open ended tube rotatable with the shaft to cause lubricant to be continuously fed from a reservoir adjacent the lower end of the tube to the upper end of the tube whereby lubricant is fed continuously upwardly through the tube and when a critical speed is attained, the lubricant rises sufficiently high in the tube to be fed out from the top end to spray against the lower portion of an upper bearing, which oil then drains downwards toward and through a lower bearing as it returns by gravity to the reservoir.
Present day drilling operations are extremely expensive, and an effort to increase the overall efficiency of the drilling operation while minimizing expense requires the essentially continuous operation of the drilling rig. Thus, it is imperative that downtime be minimized.
In this regard, there is a need for improved sealing, lubricating and cooling of bearings to maximize the useful life of the bearings. Seals for such bearings must effectively preclude the intrusion of well fluids or debris while at the same time insuring retention of the bearing lubricant. To further minimize downtime, it would be highly desirable if the rotating head were capable of cooperating with drill pipe of diverse outer diameter, thereby eliminating the need to shut down to change stripper rubbers.